MODIFIED-ATMOSPHERE PACKAGING OF BLUEBERRY FRUIT - MODELING RESPIRATION AND PACKAGE OXYGEN PARTIAL PRESSURES AS A FUNCTION OF TEMPERATURE

A mathematical model was developed to characterize the interaction of fruit O2 uptake, steady-state O2 partial pressures in modified-atmosph ere (MA) packages ([O2]pkg), and film permeability to O2 (P(O2)) from previously published data for highbush blueberry (Vaccinium corymbosum L. 'Bluecrop') fruit held between 0 and 25C. O2 uptake in nonlimiting O2 (R(O2)max,T) and the [O2]pkg at which O2 uptake was half-maximal ( K-1/2(T)) were both exponentially related to temperature. The activati on energy of O2 uptake was less at lower [O2]pkg and temperature. The predicted activation energy for permeation of O2 through the film (E(a )PO2, kJ.mol-1) required to maintain close-to-optimum [O2]pkg across t he range of temperatures between 0 and 25C was almost-equal-to 60 kJ.m ol-1. Packages in which diffusion was mediated through polypropylene o r polyethylene would have E(a)PO2, values of almost-equal-to 50 and 40 kJ.mol-1, respectively, and would have correspondingly greater tenden cies for [O2]pkg to decrease to excessively low levels with an increas e in temperature. Packages that depend on pores for permeation would h ave an E(a)PO2 of <5 kJ.mol-1. Our procedure predicted that, if allowe d to attain steady-state conditions, packages with pores and optimized to 2 kPa O2 at OC would become anaerobic with as little as a 5C incre ase in temperature. The results are discussed in relation to the risk of temperature abuse during handling and marketing of MA packaged frui t and strategies to avoid induction of anaerobiosis.